graph TB
A["🔬 Research Designs<br/>for Political Science"]
A --> B["🎯 Experimental<br/>Designs"]
A --> C["🔍 Observational<br/>Causal Designs"]
A --> D["📊 Observational<br/>Descriptive Designs"]
B --> E["🎲 Survey<br/>Experiments"]
B --> F["⚖Lab<br/>Experiments"]
C --> H["🌿 Natural<br/>Experiments"]
C --> I["📈 Regression<br/>Discontinuity"]
C --> J["⏱️ Difference-in-<br/>Differences"]
D --> K["📋 Cross-sectional<br/>Surveys"]
D --> L["📚 Case<br/>Studies"]
D --> M["🔄 Panel<br/>Studies"]
classDef startNode fill:#1a2332,stroke:#4fc3f7,stroke-width:3px,color:#e3f2fd
classDef easyNode fill:#1b2d1b,stroke:#4caf50,stroke-width:2px,color:#e8f5e8
classDef endNode fill:#1a2332,stroke:#00bcd4,stroke-width:3px,color:#e3f2fd
classDef difficultNode fill:#2d1b17,stroke:#ff9800,stroke-width:2px,color:#fff3e0
class A startNode
class B,E,F,G easyNode
class C,H,I,J endNode
class D,K,L,M difficultNode